1. Field of the Invention
The present invention relates to a punch press provided with a function for forcing out a slug punched out during a punching process.
2. Description of the Prior Art
A conventional punch press that prevents a punched out slug from popping up from the die holder during punch processing by connecting passages in the ram and the punch to form a single passage for flowing high-pressured air in order to force out the slug has been proposed. When the ram nears its dead bottom position, the passage inside the ram connects with the passage formed inside the ram guide, and compressed air is discharged from the bottom of the punch. The force of this air ejection prevents the slug from popping up as the punch is relifted, and causes the slug to drop out.
However, sometimes air ejection at the predetermined dead bottom position is insufficient to prevent the slug from popping up. Moreover, if the height of all the punches in the punch press are not constant, even if the ram is arranged such that air discharge occurs when the ram reaches its dead bottom position, optimal timing of the air discharge (optimal timing in order to prevent the slug from popping up, or in other words, discharge timed to the punching action) differs with each different punch. Further, even if punches of a uniform height are used, when some punches are shortened due to abrasion and repeated use, the height at which the end of the punch and the surface of the die meet and the set punching height may differ, causing the air ejection to occur before the punch hits the work, and causing the force of the air discharge to be insufficient to effectively prevent the slug from popping up. The slug can be prevented from popping up by flowing a constant stream of air through the punch, but this wastes most of the air and is not very economical.
In order to solve this problem, a means to detect the strike position of the ram, and to open and close a valve in response to the signal detected has been proposed. However, since accurate timing is necessary to supply air to the punch when the ram strikes the punch, a quick-response valve must be provided, increasing the cost of the punch press.